Generally, personal computers are intended to be provided with accessories such as i.a. insertable boards or expansion boards for different functions such as typically for connection of a displaying monitor, i.e. to provide graphical displaying, for communication for instance through a modem or with a local network, for driving loudspeakers. The insertable boards are inserted in specially formed slot-shaped connectors that are generally directly mounted to the motherboard of the personal computer. The short side of an insertable board can carry connectors for a communication with the exterior and these connectors are then attached to a narrow back plate or shielding or covering plate of metal, that is mounted in an opening in the housing of the computer. The back plate has a bent top part that can be screwed to a frame at the opening and it is more narrow at its lower part where it can be inserted in a slot in the frame. For slot connectors in which no expansion board has been mounted simple back plates made of sheet metal are used, “dummy cover plates” or “idling cover plates”, having no connectors and having no electric connections. In the case where there are high requirements on the electrical shielding of the circuits of the computer these back plates must well cover the opening in the computer box and furthermore, they must be in a good electrical contact with the material of the box. The latter condition is also true for the frame at the opening in which the back plates are attached.
In U.S. Pat. No. 5,929,376 a pressed plate 12 mounted in an instrument casing 10 is disclosed. The plate has in turn openings for expansion boards provided with back plates. Furthermore, springs 54, 54′ are provided to connect an inserted back plate to the shaped plate 12. The springs have contact tongues acting against a large surface of the back plates belonging to inserted boards. This has a disadvantage by the fact that a lower pressing force and thereby a worse electrical contact can be obtained at the center of the back plate, see col. 3, lines 11–16. Therefore, reinforcement rods 72 for the springs are provided.
In German published Patent Application No. 39 07 412 a housing is disclosed consisting of a socket 1 for mounting it to a wall of a room and a plurality of identical frame part that are attached to the socket and at the sides of each other and that themselves form the housing. The space formed in each frame part can be closed by front and rear caps 30, 28. The spaces are not intended for expansion boards having back plates. The disclosed housing is a modularly conducted housing intended to accommodate simple boards for internal connections.
In the published International Patent Application No. WO 93/20676 a contact spring for shielding between housing elements of electronic equipment is disclosed. The spring has two legs that have different lengths and are connected by a cylindrical portion and they are bent towards each other so that a profile approximately as the FIG. 9 is obtained. The shorter leg has outermost a portion which is bent in an angle and is intended to enter an opening in a housing flange to maintain the spring in place. The bent portion of the spring is furthermore intended to come in mechanical and electric contact with an adjacent housing flange and then acts with a pressing force against the large surface of this flange.
Apparatus housings having openings for expansion boards are also disclosed in U.S. Pat. Nos. 5,579,210, 5,679,993, 5,820,171, 4,873,395, 5,004,867, 4,924,355 and the published European Patent Application No. 0 723 389. Contact springs for electric contact and shielding are disclosed in U.S. Pat. Nos. 5,539,149, 5,952,608 and German Patent Document 196 44 417.